Radio communication system



Feb. 16, 1932. PORTS 1,844,973

RADIO COMMUNICATION SYSTEM Filed Oct. 24. 1929 H55 u I 0 7 0 1 14 25 wa, I 03 A T T HPF} LP/g DM, AR,

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I A r a/awn Patented Feb. 16, 1932 UNITED STATES PATENT OFFICE EARL G.PORTS, OF WOODSIDE, NEW YORK, ASSIGNOR TO BELL TELEPHONE LABORA- TORIES,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK RADIOCOMMUNICATION SYSTEM Application filed October 24, 1929. Serial No.402,005.

This invention relates to carrier signaling systems and more especiallyto systems of the type in which the unmodulated carrier wave componentis suppressed.

It is well known that in carrier systems suppression of the unmodulatedcarrier component results in a very material saving of the powernecessary at the transmitting station. Suppression of one side band ofthe products of modulation results in a further saving of power.However, in either case it is necessary for detection at the receiverthat oscillations of carrier frequency or oscillations having a fixedfrequency relative to the carrier generated at the transmitting stationbe introduced to combine with the incoming signal modulated components.

In carrier telephone systems it is especially important to maintain afixed frequency relation between the transmitting carrier and theintroduced oscillations. If the frequency of either the transmittingcarrier wave or that of the wave introduced at the receiving stationvaries from its fixed value,

. the efficiency of transmission is materially reduced. Thisinefficiency may be due to the loss of naturalness in the tonestransmitted or, in the case of a heterodyne system, to the factthat theresultant intermediate frequency wave differs in frequency from that forwhich the intermediate frequency amplifiers and circuits are designedwhereby a loss in output level is occasioned and distortion of the wavemay occur.

Considerable difiiculty has been experienced in maintaining theoscillations locally produced at the receiver at a fixed frequency withrespect to the carrier wave generated at the transmitter. Systems haveheretofore been proposed to automatically control the frequencyrelations between the transmitted carrier wave and the oscillationslocally supplied at the receiving station but such systems have not beenentirely satisfactory because the control function is only effected whenno messages are being transmitted. In all of these systems control ofthe frequency relation occurs at definite intervals rather widely spacedas to time. With such systems, the relationship between the frequenciessupplied at the transmitter and receiver may be correct at the beginningof a message period but before the transmission has been completed, thefrequency of one or the other of the supply sources may have varied fromits original value to such an extent that the transmission efficiencyhas been materially reduced.

An object of this invention is to provide a method of and means forimproving transmission in a carrier signal system.

Another object is to cause the frequency control function to beeffective automatically and from time to time during a message period.

Still another object is to permit frequency control to be eflectedduring individual message periods.

The above objects are accomplished in one embodiment of the invention,by providing means whereby the synchronizing mechanism is brought intooperation during momentary pauses in a message period.

More specifically, means are provided whereby during a pause betweenimpulses, constituting elements of a message, a control wave is suppliedto the transmitter and is transmitted in place of the signals. Thecontrol wave may lie either within or outside the audible range.

\Vhen transmission of the message impulses begins again, the mechanismsupplying the control wave is disconnected from the transmitter untilthe next pause occurs, when it again becomes active to supply thecontrol wave to the transmitter.

At the receiving station the control frequency wave is reproduced and ifadjustment is necessary, is used to control the actuation of a frequencychanging device in the local oscillator circuit.

Other features of the invention will be apparent from the followingdescription in connection with the accompanying drawings, Fig. 1 ofwhich shows schematically one embodiment of the invention in which thecontrol wave has a frequency within the audible range, while Fig. 2 is asimilar illustration in which the control wave has a frequency at theupper limit or outside the audible range.

Referring to Fig. 1, a transmitting station according to this inventionis illustrated schematicall at T while a cooperating receiving stationis illustrated schematically at R The various component parts of thesystem are represented by blocks, since the structure of such parts iswell known and may vary as to details but will remain within the scopeof the invention.

It is also to be understood that whereas the invention is to bedescribed in connection with a radio system, it is not necessarily solimited and may be a plied to any system using a carrier wave ortransmission purposes whether over wires or not, in which it isnecessary to introduce a wave at the receiving station having afrequency fixed relatively to that of the transmitting carrier to enabledetection of the signals.

A radio transmitting system 6 associated with antenna 7 is adapted fortransmitting messages in the well known manner. For this purposetransmitter 6 comprises the usual high frequency source, modulator, highand low frequency amplifiers and other necessary equipment, the detailsof which are not essential to an understanding of the present invention.

The synchronizin tone which is assumed to be within the au ible range isgenerated in any desired manner by source 5. For the purposes of thepresent description, the frequency of the synchronizing wave has beenchosen as 1000 cycles.

A time delay circuit D and an amplifier rectifier AR are associated withline wires 8 on which are impressed the speech or other signal waves tobe transmitted as modulw tions of the carrier wave. Relay 9 isassociated with amplifier rectifier AR for a purpose and in a mannerwhich will appear hereinafter.

At the receiving station R an antenna 10 is associated with radioreceiver apparatus 12 adapted to receive, amplify and detect theincoming wave consisting of a single side band transmitted from T Thelocal wave essential to detection is generated by source 11 andimpressed on receiver 12 over circuit 13. Source 11 may comprise avacuum tube oscillator of the type disclosed in Hartley Patent1,356,763, October 26, 1920, having one element of the frequencydetermining circuit variable to permit of adjustment as will appearhereinafter. The invention however is not to be so limited but any wavesource which may be varied as required may be utilized. The output ofreceiver 12 is impressed upon circuit 14 with which there is associated,as shown, a filter arrangement adapted to pass waves of all frequenciesexcept those between 990 cycles and '1010 cycles.

An amplifier rectifier AR is associated with the filter arrangement BFand has associated with it two relays 15 and 16.

Also associated with circuit 14 is a delay circuit D the output of whichis impressed upon low pass and high ass filters LPF and I-IPFrespectively through armature and contact of relay 15. Each of thefilters LPF and HPF has an amplifier rectifier AR and AR respectivelyassociated with it.

Magnets 17 and 18 are connected to the output of amplifier rectifiersAR, and AR, respectively. Magnets 17 and 18 are associated with discs 19and 20 which are mounted on shaft 21 so that the discs may slide alongthe shaft but are keyed to it for rotation. The magnets are supportedindependently of shaft 21 and may be desi ed to permit shaft 21 to passfreely throug them. If desired the magnets may be mounted adjacent theshaft but offset therefrom. Springs 27 or equivalent means, are providedto return discs 19 and 20 to their normaldpositions when the associatedmagnets are eenergized.

A motor M drives constantly rotating disc 22 so positioned in relationto discs 19 and 20 that a slight movement of either disc 19 or 20 willcause it to contact with the edge of disc 22 whereby shaft 21 may becaused to rotate in a direction depending upon which disc contacts withdisc 22.

. A direction changing and speed reduction gear arrangement 23 connectsshaft 21 in power driving relation to shaft 24 which in turn operates afrequency determining element of the local wave source 11.

It is to be understood that the arrangement of magnets, discs, etc. bymeans of which the outputs of amplifier rectifiers AR and AR, controlthe frequency of the wave generated at 11 is merely indicative and thatany other method of accomplishing the same result may be used and stillbe within the scope of the. present invention.

A second delay circuit D is also associated with circuit 14substantially as shown for a purpose which will appear hereinafter.

Line wires 25 upon which the output of delay circuit D is impressedcarry the signals to any desired point for their proper utilization.

The operation of the system of Fig. 1 is as follows:

As shown, relay 9 is in the released or unoperated position andtherefore the 1000 cycle synchronizing wave generated by source 5 isimpressed on the transmitter 6 over a circuit completed through thearmature of relay 9. In transmitter 6 the 1000 cycle wave modulates thecarrier wave and there is roduced in the transmitter output circuit asingle side band of the products of modulation which is impressed onantenna 7.

When speech or other signal waves are impressed on conductors 8, part oftheir energy ICC passes through amplifier rectifier AR where the energyis amplified and rectified. The

output of AR energizes relay 9 whereupon its armature breaks thesynchronizing wave contact and closes the circuit from the delay circuitD to the transmitter 6 where modulation, etc., occurs and a single sideband of the products of modulation is impressed on antenna 7 Delaycircuit D functions to delay the transmission of the signals long enoughto permit relay 9 to operate so that no part of the message is lost.

When a pause occurs during ordinary con- 15 versation or in thetransmission of other signals, relay 9 becomes deenergized and thesynchronizing wave is again transmitted. This condition continues untilconversation is resumed or the sending of signals begins agan.

At R considering first the condition when the synchronizing wave isbeing transmitted, the single side band is received by antenna 10 andimpressed on receiver 12 where it is combined with the wave from source11 and demodulated and the resultant signal wave is impressed on circuit14..

Band filter BF is adjusted to pass all frequencies except those between990 cycles and 1010 cycles (synchronizing waves 1000 cycles). Thereforewhen only the synchronizing wave is being received, relays 15 and 16remain unoperated and the output of delay circuit D is impressed uponLPF and HPF and the output circuit of delay circuit D remains open.

Delay circuit D passes the demodulated output currents from receiver 12through armature and contact of relay 15 into LPF and HPF LPF passesfrequencies of 998 cycles and below, while HPF passes frequencies of1002 cycles and above. If the output of receiver 12 lies between 998 and1002 cycles, source 11 is generating a wave of a frequency suflicientlyclose to that desired to warrant no change in its adjustment.

If, however, the frequency of the wave from receiver 12 is below 998 orabove 1002 cycles, it indicates that the frequency of the wave fromsource 11 has varied from its desired value far enough to requireadjustment.

Assuming that the lower, or difference, side band is transmitted aftermodulation with the control wave, consider the case when the frequencyis below 998 cycles which indicates that the wave from source 11 is morethan 2 cycles below its desired value. This frequency will pass low passfilter LPF and will not pass through HPF This wave is amplified andrectified in AK. and the rectifiedenergy is impressed on electromagnet17.

Magnet 17- attracts its associated disc 19 to cause it to contact withconstantly rotating (3 disc 22 whereby disc 19 and shaft 21 are causedto rotate. By means of reduction ear, etc. 23 and shaft 24, themotion ofsha t 24 is transferred to a frequency determining element in the tunedcircuit of source 11 whereby the source 11 is adjusted to its correctvalue.

When the correct frequency value of source 11 is attained no energypasses LPF and AB hence magnet 17 releases, disc 19 returns to itsnormal position under the action of springs 27 or equivalent means andshaft 21 ceases to rotate.

The same general action occurs if the output of receiver 12 is above1002 cycles, in connection with HPF AR magnet 18 and disc 20. In thiscase the rotation of shaft 21 is the reverse of that in the former caseand the frequency adjusting element is moved in the opposite direction.

When speech or other signals are sent from T and received at R signalsare impressed on circuit 14. Band filter BF passes all frequenciesexcept those between 990 and 1010 cycles. Some of the signal energytherefore passes BF and is amplified and rectified in AR The rectifiedenergy energizes relays 15 and 16. The armature of relay 15 is movedfrom its associated contact to open the circuit of the frequencyadjusting means. Any signal frequencies which lie in the band whichwould cause the operation of the frequency adjusting means are delayedin delay circuit D long enough to permit relay 15 to operate.

When relay 16 operates, its armature makes contact with its associatedcontact closing the output circuit of delay circuit D through conductors25. The signals are delayed in D long enough to permit relay 16 tooperate.

Conductors 25 may transmit the signal to a central oflice fordistribution to subscribers, etc., or to a local recording or indicatingdevice as desired.

When a pause occurs in the transmission of signals relays 15 and 16become deenergized and the system returns to the condition for utilizingthe synchronizing wave, which condition is maintained until signals areagain received.

Fig. 2 illustrates schematically a system similar to that of Fig. 1 butin which the synchronizing wave has a frequency above audibility. Thesame indices have been applied to like parts in the two figures. In Fig.2 the operation and construction of T is identical to that of Fig. 1except that source 5 is assumed to generate a wave of 10,000 cycles.

At R Fig. 2, delay circuit D is replaced with a high pass filtefHPlE"and a demodulator DM The band filter BF is replaced with a low passfilter LPF Relay 15 of Fig.

1 is not required. The local generating source and frequency ad ustingapparatus are identical to those shown within the rectangle of Fig. 1and are indicated by block LSFA k With a synchronizing wave frequency of10,000 cycles the high pass filter HIF 1s arranged to pass waves offrequencles above 9500 cycles. Associated with demodulator DM is anenergy source 26 which generates a wave havin a frequenc of 10,500cycles, low

ass filter L ldF passes requencies below 498,

igh pass filter HPF passes frequencies above 502 cycles and low passfilter LPF passes frequencies up to 9500 cycles.

The 0 eration of R of Fig. 2 is as follows:

The single side band transmitted from T is received on antenna 10 andimpressed on receiver 12 where, by means of the locally generated wavefrom LSFA the synchronizing wave of 10,000 cycles is detected andimpressed on circuit 14.

The 10,000 cycles wave cannot pass filter LPF hence relay 16 remains inthe unoperated position and the output circuit of delay circuit Dremains open. The synchronizing wave however, does pass HPF and isimressed on demodulator DM where it is comiiined with a 10,500 cyclewave and the difference frequency is selected.

If the: difference frequency is less than 498 cycles it passes LPF ifmore than 502 cycles, it passes HPF The adjustment of the 10- callygenerated wave is accomplished in the same manner as in Fig. 1.

IVhen speech or other signal waves of a frequency less than 10,000cycles are transmitted and after detect-ion impressed upon circuit 14,they pass LPF and after amplification and rectification in AR energizerelay 16. The armature of relay 16 then makes contact with itsassociated contact to close the output circuit of delay circuit D andthe detected signals are transmitted wherever desired over wires 25.

As in Fig. 1, the delay circuit D operates to delay the passage of thewaves until relay 16 is operated.

When a pause occurs in the transmission of the signals, no energy isavailable to retain relay 16 operated and while the synchronizing waveis performing its function, the output circuit 0 delay circuit D remainsopen.

It is to be understood that the frequencies given in the abovedescription are not to be considered essential to the operation of thesystem but that waves of any frequencies may be used in accordance withthe principles of the invention. I

It is also to be understood that many modifications may be made in theapparatus described and that the invention is to be limited onl by thescope of the appended claims.

W hat is claimed is:

1. In a carrier communication system the method of synchronizing a wavelocally generated at the receiving station with the carrier wavegenerated at the transmitting station which comprises automaticallytransmitting a control wave during pauses which occur during messagetransmission periods, receiving said control wave and utilizing saidwave to automatically control the frequency of the wave local to thereceiving station.

2. In a carrier communication system comprising a transmitting and areceiving station in which the unmodulated component of the products ofmodulation is suppressed at the transmitting station, means forintroducing at the receiving station a wave used for detection purposeshaving a frequency definitely related to that of the unmodulatedsuppressed wave, and means automatically operative during pauses whichordinarily occur during message transmission periods for controlling thefrequency of the wave introduced at the receiving station.

3. In a carrier communication system comprising a transmitting and areceiving station, means at the transmitting station for suppressing theunmodulated component of the products of modulation, means at thereceiving station for introducing a wave having a definite frequencyrelation to the suppressed unmodulated component, and meansintermittently automatically operative to maintain said frequencyrelation fixed.

4. A carrier communication system in accordance with claim 3,characterized in this that means are provided whereby said automaticallyoperative means are caused to function during pauses which occur duringmessage transmission periods.

5. In a carrier communication system, a transmitting station and areceivin station, means at the transmitting station or introducing awave having a definite frequency relation to the suppressed unmodulatedcomponent, means at the transmitting station for intermittentlytransmitting a wave of constant frequency, and means at said receivingstation for receiving said constant frequency wave and utilizing it tomaintain the frequency relation fixed between the suppressed componentand the introduced wave.

6. A carrier communication system in accordance with claim 5,characterized in this that means are provided whereby said constantfrequency wave is transmitted during pauses which occur during messagetransmission periods.

7. A carrier communication system comprising a transmittin station and areceiving station, means at t e transmitting station for suppressing theunmodulated component of the products of modulation, means at thereceiving station for introducing a wave having a definite frequencyrelation to the suppressed component, means at the transmitting stationfor intermittently transmitting a wave of constant frequency, means atthe receiving station for receiving and detecting the wave correspondingto said constant frequency wave, and means automatically operative tovary the frequency of said introduced wave in accordance with thevariation of the frequency of the detected wave corresponding to saidconstant frequency wave from the frequency of the transmitted constantfrequency wave.

8. A carrier communication system in accordance with claim 7,characterized in this that said automatically operated means functionsduring pauses which occur during messa e transmission periods.

n witness whereof, I hereunto subscribe my name this 23 day of October1929.

EARL d. PORTS.

